1. Field of the Invention
The present invention relates to a microscope illumination device.
2. Description of the Related Art
Conventional microscopes commonly employ individually a microscope illumination device comprising a Koehler illumination. In the Koehler illumination, there is a slight non-uniformity in terms of the light distribution characteristic of a light source, while there is no non-uniformity corresponding to the brightness distribution in terms of the position within the light source. Therefore, the illumination is popular as an optimal illumination device with little non-uniformity in illumination.
In recent years, however, technological improvements in and the popularization of photoelectric conversion elements such as charge-coupled device (CCD) and the like has caused imaging in digital images to become a common practice in the field of microscopy as well. As a result, even a slight illumination non-uniformity that is not apparent in a visual observation is conspicuous.
A known technique to alleviate such illumination non-uniformity is a technique utilizing a fly-eye lens. For example, Laid-Open Japanese Patent Application Publication No. 2002-006225 and Laid-Open Japanese Patent Application Publication No. 2005-043517 have disclosed a microscope illumination device equipped with a fly-eye lens at the rear focal position of a collector lens. This microscope illumination device projects a quasi surface illuminant formed in the fly-eye lens element of the fly-eye lens onto an aperture stop and projection lens, thereby eliminating the illumination non-uniformity corresponding to the light distribution characteristic of a light source.
An illumination optical system employing a fly-eye lens is more complex than a common illumination optical system. As a result, the illumination light is sometimes partially broken in the midst of the light path before the illumination light is projected on a specimen surface.